Stylet-free epidural catheter and thread assist device

ABSTRACT

A stylet-free epidural catheter for insertion into a patient via a needle defining proximally a needle hub and distally a needle tip, includes a catheter having a proximal end, a distal end, and a body connecting the ends. The body defines therealong a stiffening section of a predetermined length disposed a predetermined distance proximally of the distal end such that it is located generally about an area where the body approaches a needle hub when the distal end approaches a needle tip. The stiffening section has a flexural stiffness at least twice that of the remainder of the body. A thread assist device to reduce buckling of a catheter being inserted through a needle, includes a body defining a TAD proximal end, a TAD distal end substantially spaced apart along a longitudinal axis from the TAD proximal end, and a TAD sidewall connecting the TAD ends. The TAD distal end is configured and dimensional for at least partial receipt and releasable maintenance within a hub of a needle, and the TAD sidewall is configured and dimensioned intermediate the TAD ends to enable axial sliding manipulation of the catheter through the needle hub by a user. The TAD ends substantially preclude non-axial movement of the catheter at the TAD ends and the TAD sidewall limits non-axial movement of the catheter between the TAD ends.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a divisional of U.S. patent application Ser. No.09/703,892, filed Nov. 1, 2000.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a stylet-free epidural catheterfor insertion into a patient via a needle, as well as a thread assistdevice, both to reduce buckling of a catheter in and around the needlehub, and more particularly to a combination of such an epidural catheterand such a thread assist device.

[0003] Commonly assigned U.S. Pat. No. 5,947,940 entitled “CatheterReinforced to Prevent Lumenal Collapse and Tensile Failure Thereof” isincorporated herein by reference. This patent discusses in detail theproblems associated with medical catheters, and in particular anepidural catheter, and the need for reinforcement thereof to meet therigorous requirements of an epidural catheter. The reinforcementdisclosed is at least one helical reinforcing member (preferablypredominantly non-metallic) wound around the longitudinal axis of theelongated tubular body of the catheter for reinforcing the body toprevent radial collapse thereof during bending and pinching thereof andto prevent longitudinal breakage thereof under tension. Such cathetershave proven to be quite satisfactory in use and, in particular, asepidural catheters.

[0004] Nonetheless, the design of the catheter described above hasproven to be less than totally satisfactory. Typically, the use of astylet within the catheter is still required during the insertionoperation. From the point of view of the catheter manufacturer, thisresults in additional costs, both for the manufacture of the stylet andfor the insertion of the stylet through the catheter. From the point ofview of the catheter user, an additional step in the procedure isrequired to ultimately withdraw the stylet from the catheter after thestylet has served its function of stiffening the catheter sufficientlyto allow it to enter the epidural space (the ligamentum flavum). Due tothe length of the stylet, this is a time-consuming and laboriousoperation step. Furthermore, the removed stylet is a contaminated“sharp” which must be safely and specially disposed of in order to notexpose room personnel to additional risks of contamination.

[0005] The prior art also teaches thread assist devices (TADs) whichenter into the luer hub of the needle and preclude buckling (non-axialor lateral collapse) of the catheter just as the catheter distal tip isemerging from the distal end of the needle into the epidural space, atime when buckling tends to occur due to the additional resistanceexerted by the ligaments of the epidural cavity. The known TADs precludebuckling of the catheter in the region of the needle hub by completelysurrounding the catheter sidewall so that there is no room in which thecatheter can buckle. On the other hand, this positioning of the TADrequires a practitioner to move the catheter forwardly through theneedle from a point of contact (between the practitioner and thecatheter) which is disposed proximally of the needle hub; this makes itmore difficult for the surgeon to introduce a substantially straight orlinear length of the catheter into the needle hub. At the very time thatthe practitioner is pressing on the catheter with his fingers and usingfriction (between his fingers and the catheter) to slide the catheterforwardly through the TAD and the needle, there is a tendency for thepractitioner to laterally deflect the catheter before it enters the TADso that it is no longer in axial alignment with the needle and the TAD.Thus, the need remains for a TAD for use with an epidural catheter(whether reinforced or not) which enables movement of the catheterslidingly along the needle without deflecting the catheter from theneedle axis.

[0006] Accordingly, it is an object of the present invention to providea catheter which does not require a stylet for the insertion operation.

[0007] Another object is to provide such a catheter which is economicalto produce.

[0008] A further object is to provide a thread assist device (TAD) tofacilitate passage of a catheter through a needle.

SUMMARY OF THE INVENTION

[0009] In one aspect, the present invention relates to a stylet-freecatheter for insertion into a patient via a needle, wherein the needledefines proximally a needle hub and distally a needle tip. The cathetercomprises a proximal end, a distal end, and a body connecting theproximal and distal ends. The body defines therealong a stiffeningsection of a predetermined length disposed a predetermined distanceproximally of the distal end such that it is located generally about anarea where the body approaches the needle hub when the distal endapproaches the needle tip. The stiffening section has a flexuralstiffness at least twice that of the remainder of the body.

[0010] In a preferred embodiment, the stiffening section has a length ofabout 5 (preferably 7) cm, disposed from about 10 cm to about 15 cmproximally of the distal end, and has a diameter not exceeding thediameter of the remainder of the body by more than about 0.15 mm.

[0011] In one preferred embodiment, the stiffening section is formed ofplastic tubing and a cured adhesive extending circumferentially aboutthe plastic tubing to provide a stiffening coating. The cured adhesivepreferably is UV-cured in situ. In an alternatively preferredembodiment, the stiffening section is formed of plastic tubing and aplastic sleeve heat-shrunk about the plastic tubing to stiffen theplastic tubing. The sleeve is preferably polyethylene terephthalate(PET). In both preferred embodiments, the stiffening coating/sleeve isnon-tacky and wear-resistant, has a thickness not exceeding about 0.08mm, extends in a substantially uniform thickness along the stiffeningsection and about the plastic tubing, and reinforces the plastic tubingof the stiffening section.

[0012] The present invention also encompasses in combination such acatheter and a needle defining proximally a needle hub and distally aneedle tip.

[0013] The present invention further encompasses a thread assist deviceto reduce buckling of a catheter being inserted through a needle. TheTAD comprises a body defining a proximal end, a distal end substantiallyspaced along a longitudinal axis form the proximal end, and a sidewallconnecting the proximal and distal ends. The TAD distal end isconfigured and dimensioned for at least partial receipt and releasablemaintenance within a hub of a needle, and the TAD sidewall is configuredand dimensioned to enable axial sliding manipulation of a catheterthrough the needle hub and through the needle by a user. The TADproximal and distal ends substantially preclude non-axial or lateralmovement of the catheter at the TAD ends, and the TAD sidewall limitsnon-axial or lateral movement of the catheter between the TAD ends. In apreferred embodiment, the TAD sidewall is generally cylindrical butextends no more than 180° about the TAD body intermediate the TADproximal and distal ends to define a gap intermediate its long edgessuch that a user can establish axial sliding manipulation of thecatheter through the gap and further limit non-axial movement of thecatheter between the TAD ends.

[0014] In another embodiment, the TAD sidewall extends over an arc of nomore than about 90° about the TAD body intermediate the TAD ends and isslightly bowed outwardly from the TAD longitudinal axis forsubstantially the entire length of the TAD sidewall along the catheter,thereby to increase the potential extent of contact between the user andthe catheter between the TAD ends and thus facilitate grasping andgenerally axial movement of the catheter through the TAD by the user.

[0015] The present invention also encompasses in combination such threadassist device, a catheter, and a needle, the distal end of the TAD beingat least partially disposed in the hub of the needle, and the catheterextending through the TAD proximal end, along the TAD sidewall, throughthe TAD distal end and into the needle.

[0016] Further, the present invention specifically encompasses thecombination of such a catheter and such a TAD.

BRIEF DESCRIPTION OF THE DRAWING

[0017] The above and related objects, features, and advantages of thepresent invention will be more fully understood by reference to thefollowing detailed description of the presently preferred, albeitillustrative, embodiments of the present invention when taken inconjunction with the accompanying drawing wherein:

[0018]FIG. 1 is a fragmentary exploded side elevational view of astylet-free epidural catheter according to the present invention;

[0019]FIG. 2 is a sectional view thereof taken along the line 2-2 ofFIG. 1;

[0020]FIG. 3 is a fragmentary assembly side elevational view of thecatheter rotated 90° about its axis from FIG. 1;

[0021]FIG. 4 is a sectional view thereof taken along the line 4-4 ofFIG. 3;

[0022]FIG. 5 is a sectional view thereof taken along the line 5-5 ofFIG. 4;

[0023]FIG. 6 is a sectional view taken along the line 6-6 of FIG. 5;

[0024]FIG. 7 is a fragmentary exploded side elevational view of a threadassist device according to the present invention;

[0025]FIG. 8 is a sectional view taken along the line 8-8 of FIG. 7;

[0026]FIG. 9 is a fragmentary assembly side elevational view of the TADrotated 90° about its axis from FIG. 7;

[0027]FIG. 10 is a sectional view thereof taken along the line 10-10 ofFIG. 9;

[0028]FIG. 11 is a sectional view thereof taken along the line 11-11 ofFIG. 10;

[0029]FIG. 12 is a view similar to FIG. 10, but of another embodiment ofthe TAD; and

[0030]FIG. 13 is a sectional view thereof taken along the line 13-13 ofFIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring now to the drawing, and in particular FIGS. 1-6thereof, therein illustrated is a stylet-free epidural catheteraccording to the present invention, generally designated by thereference numeral 10. The catheter 10 is designed for insertion into apatient via a needle, generally designated 12, defining proximally aneedle hub 14, distally a needle tip 16 and optionally a pair of wings17.

[0032] In its conventional aspects, the catheter 10 includes a proximalend 22, a distal end 24 and a body section, generally designated 26,connecting the proximal and distal ends 22, 24.

[0033] In its novel aspects, the body 26 of catheter 10 definestherealong a stiffening section, generally designated 30. The stiffeningsection 30 is of a predetermined length (preferably about 5 cm) and isdisposed a predetermined distance proximally of the distal end 24(preferably from about 10 cm to about 15 cm proximally of the distalend) such that it is located generally about an area where the catheterbody 26 approaches the needle hub 14 when the catheter distal end 24approaches the needle tip 16. This is a critical point in thefunctioning of the epidural device because, as the catheter distal end24 begins to emerge from the distal needle tip 16, it encountersresistance which must be overcome by the surgeon sliding the catheter 10through the needle 12. The stiffening section 30 has a diameter notexceeding the diameter of the remainder of the body 26 by more thanabout 0.15 mm so that the increase in thickness at the stiffeningsection 30 is barely appreciable. As will be apparent to those skilledin the art, the length and positioning of the stiffening section 30 maybe adjusted for use in various epidural needles (for example, needlesfor different species), with the object always being that thestrengthening section will be entering the needle hub as the catheterdistal end is emerging from the needle tip.

[0034] It is a critical factor of the present invention that thestiffening section 30 has a flexural strength (that is, it resistsnon-axial or lateral bending) which is at least twice the flexuralstrength of the remainder of the catheter body 26. Flexural strength iseasily measured using an Instron Tester. A minimum doubling of theflexural strength of the stiffening section (relative to the plastictubing 32 alone of the remainder of the catheter body 26) obviates theneed to employ a stylet in order to stiffen the catheter. Nonetheless,the stiffness of the stiffening section 30 must not preclude suchbending thereof as may be necessary for it to pass through the curvedneedle tip 16. (Most needle tips are curved to facilitate passagetherethrough of the catheter.) Further, the stiffening section 30 mustnot be so thick that it cannot pass through the needle 12 (andespecially the needle tip 16).

[0035] The stiffening section 30 may be formed by various mechanisms.

[0036] In a first preferred mechanism illustrated in FIG. 1, thestiffening section 30 is formed of plastic tubing 32 (similar to theplastic tubing of the remainder of the catheter body 26) and a curedadhesive 34 extending circumferentially about the plastic tubing 32 toprovide a stiffening coating 36. Preferably the stiffening coating 36 isnon-tacky and is wear-resistant. The stiffening coating 36 preferablyhas a thickness not exceeding about 0.08 mm. Ideally, the stiffeningcoating 36 extends in a substantially uniform thickness along thestiffening section 30 and about the plastic tubing 32, so that itreinforces the plastic tubing 32 of the stiffening section 30. The curedadhesive is preferably a UV (ultraviolet)—cured adhesive tolerated bythe patient's body, and optimally it is cured in situ. In other words,the uncured adhesive is applied about the plastic tubing 32 of thestiffening section 30 and then cured in place using ultraviolet light.

[0037] In a second preferred mechanism also illustrated in FIG. 1, thestiffening section 30 is formed of plastic tubing 32 (similar to theplastic tubing of the remainder of the catheter body 26) and a plasticsleeve 44 heat-shrunk about the plastic tubing 32 to provide astiffening sleeve 46. As in the case of the stiffening coating 36, thestiffening sleeve 46 is preferably non-tacky and wear-resistant, has athickness not exceeding 0.08 mm and ideally extends in a substantiallyuniform thickness along the stiffening section 30 and about the plastictubing 32 so that the stiffening sleeve 46 reinforces the plastic tubing32 of the stiffening section 30. The sleeve 44 may be made of anysuitable heat-shrinkable plastic which is tolerated by the patient'sbody and provides the desired stiffening action when heat shrunk. Apreferred plastic is polyethylene terephthalate (PET).

[0038] A conventional thread assist device (TAD) 48 has a front endwhich is inserted into the needle hub 14 and a rear end which is enteredby the catheter front end 24, a length of the catheter body 26, thestiffening section 30 and more of the length of the catheter body 26.

[0039] Referring now to FIGS. 7-11 in particular, therein illustrated isa thread assist device (TAD) according to the present invention,generally designated by the reference numeral 50, to reduce buckling(i.e., lateral or non-axial collapse) of a catheter being insertedthrough a needle 12, regardless of whether that catheter is a catheter10 according to the present invention (as described hereinabove) or aconventional catheter. As the TAD 50 and stiffening section 30 serve thesame function (that is, to reduce buckling of the catheter beinginserted through the needle), typically the thread assist device findsgreatest utility in use with a conventional catheter rather than acatheter 10 according to the present invention (as the latter typicallydoes not require a TAD to be used).

[0040] The TAD 50 comprises a body, generally designated 52, defining aproximal end 54, a distal end 56, and a sidewall 60 connecting the TADproximal and distal ends 54, 56. The TAD proximal and distal ends 54, 56are substantially spaced apart along a longitudinal axis of the TAD body52 and define respective full cylinder passageways 55, 57 therethrough,respectively. The distal end 56 of the TAD body 52 is configured anddimensioned for at least partial receipt and releasable maintenancewithin a needle hub 14.

[0041] The TAD sidewall 60 is configured and dimensioned intermediatethe TAD proximal and distal ends 54, 56 to enable axial slidingmanipulation of the catheter through the needle hub 14 by a user. Moreparticularly, the sidewall 60 is generally cylindrical, but (as bestseen in FIGS. 10 and 11) extends only about 180° (and clearly no morethan 270°) about the TAD body 52 intermediate the TAD proximal anddistal ends 54, 56 thereof. Thus the TAD sidewall 60 defines a gap 62intermediate the long edges of the sidewall 60 subtending an angle ofabout 180° (and optionally less). This gap 62 is configured anddimensioned to enable a user to establish axial sliding manipulation ofthe catheter by inserting one or more fingers (or fingertips) throughthe gap 62 and against the catheter, thereby pressing the catheteragainst the TAD sidewall 60. The TAD proximal and distal ends 54, 56substantially preclude non-axial movement of the catheter at the TADends, as such TAD ends extend fully about the circumference of thecatheter portions extending therethrough. Because the pressure of theuser's finger on the catheter only presses the catheter against thesidewall 60, the finger pressure further limits non-axial movement(buckling) of the catheter between the TAD ends 54, 56. The absence ofany deflection of the catheter as it is being manipulated through theneedle 12 facilitates the manipulation process by ensuring a commonalignment of the longitudinal axes of the needle 12 and the catheterbody 26.

[0042] Referring now to FIGS. 12 and 13, therein illustrated is avariant, generally designated 50′, of the preferred TAD embodimentillustrated in FIGS. 7-11. The variant 50′ is similar to the embodiment50, except that in the variant 50′ the TAD sidewall 60′ defines a gap62′ subtending an angle of about 90° (and optionally less)—i.e., thesidewall 60′ extends circumferentially about the catheter over an arc ofno more than about 90° about the TAD body 52 intermediate the TAD ends54, 56. Furthermore, in the variant 50′, the TAD sidewall 60′ isslightly bowed outwardly from the TAD longitudinal axis forsubstantially the entire length of the TAD sidewall 60′ along thecatheter. While the TAD proximal and distal ends 54, 56 still precludebuckling of the catheter therein, the lesser arc of the TAD sidewall 60′and the spacing of the TAD sidewall 60′ from the unstressed catheterincreases the potential extent of contact between one or more of theuser's fingers and the catheter between the TAD ends 54, 56 as more ofthe catheter circumference is exposed and engageable by the user'sfingertips. Accordingly, grasping and generally axial movement of thecatheter through the variant TAD 50′ by the user is facilitated.

[0043] The TAD is preferably formed of a plastic, such as a medicalgrade thermoplastic material, which preferably exhibits a low flexuralmodulus in order to allow the TAD to be bent by the practitioner'sfinger during the placement operation. A preferred material is alow-density polyethylene.

[0044] While the drawing illustrates the reinforced epidural catheter 10in combination with a TAD 50, it will be appreciated that the TAD 50 maybe used with catheters other than the catheter 10 of the presentinvention.

[0045] To summarize, the present invention provides a stylet-freecatheter which is economical to produce. The present invention furtherprovides a thread assist device (TAD) to facilitate passage of acatheter (whether reinforced or not) through a needle.

[0046] Now that the preferred embodiments of the present invention havebeen shown and described in detail, various modifications andimprovements thereon will become readily apparent to those skilled inthe art. Accordingly, the spirit and scope of the present invention isto be construed broadly and limited only by the appended claims, and notby the foregoing specification.

I claim:
 1. A stylet-free catheter for insertion into a patient via aneedle defining proximally a needle hub and distally a needle tip,comprising: a catheter having a proximal end, a distal end, and a bodyconnecting said proximal and distal ends; said body defining therealonga stiffening section of a predetermined length disposed a predetermineddistance proximally of said distal end such that it is located generallyabout an area where said body approaches a needle hub when said distalend approaches a needle tip; said stiffening section having a flexuralstiffness at least twice that of the remainder of said body.
 2. Thecatheter of claim 1 wherein said stiffening section has a length ofabout 5 cm.
 3. The catheter of claim 2 wherein said stiffening sectionis disposed from about 10 cm to about 15 cm proximally of said distalend.
 4. The catheter of claim 1 wherein said stiffening section extendsfrom about 10 cm to about 15 cm proximally of said distal end.
 5. Thecatheter of claim 1 wherein said stiffening section has a diameter notexceeding the diameter of the remainder of said body by more than about0.15 mm.
 6. The catheter of claim 1 wherein said stiffening section isformed of plastic tubing and a cured adhesive extendingcircumferentially about said plastic tubing to provide a stiffeningcoating.
 7. The catheter of claim 6 wherein said stiffening coating isnon-tacky and wear-resistant.
 8. The catheter of claim 6 wherein saidstiffening coating has a thickness not exceeding about 0.08 mm.
 9. Thecatheter of claim 6 wherein said stiffening coating extends in asubstantially uniform thickness along said stiffening section and aboutsaid plastic tubing.
 10. The catheter of claim 6 wherein said stiffeningcoating reinforces said plastic tubing of said stiffening section. 11.The catheter of claim 6 wherein said cured adhesive is UV-cured.
 12. Thecatheter of claim 11 wherein said cured adhesive is cured in situ. 13.The catheter of claim 6 wherein said cured adhesive is UV-cured in situ.14. The catheter of claim 1 wherein said stiffening section is formed ofplastic tubing and a plastic sleeve heat-shrunk about said plastictubing to stiffen said plastic tubing.
 15. The catheter of claim 14wherein said sleeve is non-tacky and wear-resistant.
 16. The catheter ofclaim 14 wherein said sleeve has a thickness not exceeding 0.008 cm. 17.The catheter of claim 14 wherein said sleeve extends in a substantiallyuniform thickness along said stiffening section and about said plastictubing.
 18. The catheter of claim 14 wherein said sleeve reinforces saidplastic tubing of said stiffening section.
 19. The catheter of claim 14wherein said sleeve is polyethylene terephthalate (PET).
 20. A catheterfor insertion into a patient via a needle defining proximally a needlehub and distally a needle tip, comprising: a catheter having a proximalend, a distal end, and a body section connecting said proximal anddistal ends; said body defining therealong a stiffening section having alength of about 5 cm. and a diameter not exceeding the diameter of theremainder of said catheter body by more than about 0.15 mm; saidstiffening section being disposed from about 10 cm to about 15 cm.proximally of said distal end such that it is located generally about anarea where said body approaches a needle hub when said distal endapproaches a needle tip; said stiffening section being formed of plastictubing and an adhesive UV-cured in situ and extending circumferentiallyabout said plastic tubing to provide a stiffening coating, saidstiffening coating being non-tacky and wear-resistant and extending in asubstantially uniform thickness not exceeding 0.08 mm along saidstiffening section and about said plastic tubing to reinforce saidstiffening section; said stiffening section having a flexural strengthat least twice times that of the remainder of said body.
 21. A catheterfor insertion into a patient via a needle defining proximally a needlehub and distally a needle tip, comprising: a catheter having a proximalend, a distal end, and a body section connecting said proximal anddistal ends; said body defining therealong a stiffening section having alength of about 7 cm. and a diameter not exceeding the diameter of theremainder of said catheter body by more than about 0.15 mm; saidstiffening section being disposed from about 10 cm to about 15 cm.proximally of said distal end such that it is located generally about anarea where said body approaches a needle hub when said distal endapproaches a needle tip; said stiffening section being formed of plastictubing and a plastic sleeve heat-shrunk about said plastic tubing tostiffen said plastic tubing; said sleeve being non-tacky andwear-resistant and extending in a substantially uniform thickness notexceeding about 0.08 mm along said stiffening section and about saidplastic tubing to reinforce said stiffening section; said stiffeningsection having a flexural strength at least twice that of the remainderof said body.
 22. In combination, the catheter of claim 1 and a needledefining proximally a needle hub and distally a needle tip.
 23. Incombination, the catheter of claim 21 and a needle defining proximally aneedle hub and distally a needle tip.
 24. In combination, the catheterof claim 22 and a needle defining proximally a needle hub and distally aneedle tip.